Yu.E. Kirsh

Structural transformations and water associate interactions in poly-N-vinylcaprolactam–water system

Abstract Structural transformations and water associate interactions were studied in poly-N-vinylcaprolactam (PVCL)–H 2 O system by various methods (IR-spectroscopy, quantum-chemical calculations, DSC and light microscopy). A number of features of PVCL macromolecules were first found: (i) the conformation type of a side seven-member ring deduced by quantum-chemical calculations is the “chair”; (ii) the main chain of PVCL prepared by usual radical polymerization has syndiotactic structure; (iii) the calculation of charge distribution on a CO oxygen atom in the analogue of PVCL chainlink gives the large electron density value being −0.362. The addition of water to PVCL changes greatly glass transition temperature ( T g ). The DSC method shows a lowering of T g from 147° (dry polymer) to −17°÷−38° at N (number of water molecules per unit) being 2.6÷8.0. Cold crystallization and subsequent melting of ice-like units formed of water associates in the presence of PVCL macromolecules were displayed at N =8 and 10. Crystallization under cooling happens only at the increased N ( N >10). Sharp decrease of melting heat of ice-like units (Δ H mt ) from 225 to 48 J/g (334 J/g of ice in bulk water) occurs as N diminishes from 20 up to 8. PVCL macromolecules in aqueous solution are the strongest modifier of water associate structures being affected by the polarization action of high polar amide CO groups and by specific configurational and conformational structures of the polymer.

Physico-chemical study of ionic equilibria for poly-2 and poly-4-vinylpyridines in alcohol-water solutions

Abstract The ionic equilibria for poly-4-vinyl pyridine (P4VP) and poly-2-vinyl pyridine (P2VP) were studied by physico-chemical techniques such as potentiometry, viscosity and NMR- 1 H. The mixture of ethanol (45 per cent w.p.) and water was used as solvent to obtain the total range of ionization (0–1). It was found that the dissociation constants of pyridine residue of polymers in the absence of electrostatic interaction (p K 0 = 3·3–3·9) are lower than for the monomer analogues 4-ethylpyridine and 2-ethylpyridine (5·02) and depend on ionic strength (NaCl). A sharp decrease of p K app at the beginning of titration and increase of specific viscosity for P4VP and P2VP are both explained by electrostatic interactions between positive charges forming during titration of the macromolecules. Most probably, these interactions act through the organic part of the macromolecule. On the other hand, it is shown by NMR- 1 H that sharp changes in p K app and specific viscosity at the beginning of the titration are not associated with changes in the average conformation of the monomer unit in the polymer. This conformation can be destroyed only when the energy of electrostatic interactions is large enough and this occurs when the mean distance between positive charges is relatively short.

Physico-chemical properties of the copper(II)-poly-4-vinylpyridine complexes

Abstract Water-soluble Cu(II) complexes of poly-4-vinylpyridine, partially quaternized by methyl bromide or dimethylsulphate (PP, Mt) and of the analogue (4-ethylpyridine) were studied by physicochemical technique such as visible spectrophotometry, viscosity, speed sedimentation and EPR spectroscopy. Peculiarities of the complex formation reaction were observed for the polymer compared to the analogue. The predominant formation of tetrapyridinate-Cu(II) species [(CuL 4 )] 24 was found to take place in aqueous solution for PP, Mt with degree of quaternization (β) 20,24,37,49,57,65 per cent over a wide range of P Y J Cu(II) molar ratios. In addition, not all the free polymer pyridine residues are capable of forming [Cu L4 ] 2 complexes even though there is a large excess of Cu(II) ions. The maximum value of the pyridine fraction forming [Cu L 4 ] 21 in PP Y Mt-20, 24, 37, 49 (obtained by spectroscopic titration) was found to be 45–50 per cent. Addition of Cu(NO 3 ) 2 to the aqueous polymer solution causes strong reduction of specific viscosity and increase of sedimentation coefficient from - 1 S to - 6 S. These data lend to the suggestion of the existence of macromolecular associates bound by Cu(II) ions and approximate estimation of their average molecular weight. It was shown also that Bjerrums procedure cannot be used to account for the polymer stability constants. The differences between complex formation for polymer pyridine and monomer pyridine seem to be due to the high local pyridine concentration in the coil of the macromolecule and the hydration effects of the polymer chain on the characteristics of the pyridine residues.

Comparison of properties of an oxime-bound partially quaternized poly-4-vinylpyridine and a monomer analogous oxime

Abstract Six copolymers of 4-vinylpyridine and 4-vinyl-N-phenacyloximepyridinium bromide (PPyOx-12, 23, 40, 50, 60 and 72 per cent) were prepared from poly-4-vinylpyridine partially quaternized by phenacylbromide (PPyKt) and hydroxylamine. The potentiometric data of the polymer acid groups (oxime, keto-enol tautomerism) in PPyOx and PPyKt were compared with those of 4-ethyl-N-phenacyloximepyridinium bromide (PyOx) and 4-ethyl-N-phenacylpyridinium bromide (PyKt) respectively. In addition, the second-order constants of the nucleophilic reaction for all the copolymers (PPyOx) and the analogue towards p-nitrophenylacetate (NPA) were determined at various pH values in water at 25°. In contrast to the known potentiometric behaviour of polyacrylic and polymethacrylic acids, the dissociation constants (pKa) of acid groups in PPyKt and PPyOx were found to be independent of the degree of ionization. Moreover, the values of pKa of these groups for all PPyKt and PPyOx samples were appreciably less than the pKa of the corresponding analogues. As a consequence, the oxime of PPyOx-12 in the range of pH between 7·5 and 9·0 reacts about two order of magnitude faster than the monomer with the ester. These results indicate that, in contrast to the known correlation between reactivity (nucleophilicity) and basicity for monomer compounds, the activity of the polymer oxime does not diminish with a decrease of the basicity. On the contrary, the reactivity of polymer anion towards the ester is markedly higher than that of the monomer anion of PyOx. An explanation may be found in the effects of microenvironment on the property of the functional groups attached to the side pyridine residues of PVP.

Solvation effects and reactivity of free pyridine residues in macromolecules of poly-4-vinylpyridine derivatives

Abstract Water-soluble derivatives of poly-4-vinylpyridine (PVP) were prepared by means of quaternization of PVP with ethyl bromide, butyl bromide, hexyl-bromide and bromacetic acid. In addition, hydrolysis of p-nitrophenylacetate (NPA) and 3-nitro-4-acetoxybenzoic acid (NABA) catalyzed by these polymers and 4-ethylpyridine as analogue were studied spectrophotometrically both in water and alcohol-water mixtures at 25° and pH 7·8. The second-order rate of NPA hydrolysis (Kt) was independent of the length of alkyl groups and the salt concentration. While an increase of the degree of quaternization (β) for PVP derivatives resulted in a reduction of the value of Ki in water, in 37–50 vol per cent alcohol-water there was the opposite effect. At large values of β, Ki did not depend on the content of ethanol. The bell-shaped dependence of Ki on β was shown in the case of amionic NABA. The value of Ki proved to be very sensitive to both the nature of salt and the salt concentration in aqueous solution. The use of viscosity, turbidimetry and potentiometry for studying these polymers allowed the role of the quaternized pyridine residue to be elucidated. The peculiarities of the kinetic behaviour of the free basic group were explained by the hydrophilic nature of the quaternized PVP changing as the degree of quaternization is increased so causing an exclusion of the substrate molecules from the polyion.

Complexing properties and structural characteristics of thermally sensitive copolymers of N-vinylpyrrolidone and N-vinylcaprolactam

Abstract The interaction of thermally sensitive copolymers of N -vinylpyrrolidone (VP) and N -vinylcaprolactam (VC) with small molecules having different chemical structures (8-anilinonaphthalene-1-sulphonic acid magnesium salt dihydrate, acridine orange, phenol, and sodium dodecyl sulphate) in aqueous solutions was studied by luminescent methods. The interaction of these copolymers with acridine orange was studied at different temperatures. It was established that the complexing ability of VP–VC copolymers even at a low content of VC units exceeds that of poly- N -vinylpyrrolidone. At a high content of VC units, and a low content of VC units, the complexing ability of VP–VC copolymers was found to be higher than that of poly- N -vinylcaprolactam. It is shown that the change in functional characteristics of VP–VC copolymers is determined by changes in the structural organization of VP–VC macromolecules and by increasing intramacromolecular interactions between nonpolar groups. Intramacromolecular structurization occurring during temperature increase and complexation is manifested very distinctly by changes in nanosecond dynamics of macromolecules. Nanosecond relaxation times characterizing intramolecular mobility of macromolecules with increasing temperature and in complexation with phenol and surfactant ions were determined.

A study of molecular diffusion in alcohol—water solution of poly-4-vinylpyridine by fluorescence quenching

Abstract Intra- and intermolecular diffusion processes in alcohol—water solutions of poly-4-vinylpyridine (PVPy) were studied by the fluorescence quenching method. It was prepared fluorescent-labelled PVPy (PVPy-F) by copolymerizing 4-vinylpyridine with anthrylmethylmethacrylate (F) (one chromophore group per 500 chain links in the copolymer). PVPy carrying both the chromophore and quenching chain links (quaternization of the pyridine residue by dimethylsulphate) (PVPy-FQ) and PVPy carrying only the quenchers (PVPy-Q). Measurement of the mean lifetime of the excited state of the anthracene group for the polymers and for the monomer analogue (F) with increasing quencher concentration and use of the Stern-Volmer relation permit determination of the constants of bimolecular collisions between the monomer quencher (Q) (4-ethyl-N-methyl pyridinium sulphate) and F, between the monomer quencher and PVPy-F and between Q and F incorporated in the same polymer chain (PVPy-FQ). The values of the diffusion constant for the system of PVPy-F and Q and for the system of PVPy-FQ are approximately two and four times respectively less than that for the monomer pair (F + Q). For the latter system, the finding indicates some hindrance to the diffusion of the chain links with each other within the coil. Nevertheless, their mobility remains high and probably microdiffusion will not limit chemical reactions of functional groups within coils and with monomer molecules. In studying the fluorescence quenching of the chromophore for PVPy-F in the presence of the polymer quencher, it was found that mutual interpenetration of the polymer coils is intensified markedly when the solution volume is filled entirely by the swelling coils.

Chainlength effects on interactions of polyvinylpyrrolidone with low and high molecular compounds

Abstract Very narrow fractions of polyvinylpyrrolidone (PVP) for a range of low molecular weight from 20·103 to &{;10 3 were prepared by gel filtration using sephadex gel. Interactions between fractions of different Mn and small molecules (iodine and 1-anilinonaphthaline-8-sulphonate) and polymers (polymethacrylic and polyacrylic acids) were studied in aqueous solution. The ability of PVP to form complexes with low molecular weight compounds depends on chainlength. The greatest loss of the ability was observed for PVP with Mn on passing from 5·103 to &{;10 3 . The chainlength effects for PVP are accounted for an unlike dehydration and unlike “local” link concentration near links for these macromolecules in water. For PAA and PMAA. the threshold values of Mn, below which there is the beginning of weakening of complexation for PVP, are 6·103 and 2.5·103 respectively. The difference of the complex formation for these polyacids appears to be related to hydrophobic interactions between the χ-methyl groups of PMAA and nonpolar regions of PVP.

Sulfonate containing aromatic polyamides as materials of pervaporation membranes for dehydration of organic solvents: hydration, sorption, diffusion and functioning

Abstract A study of the hydration, sorption and diffusion for water and ethanol within polymer films prepared from aromatic polyamides (condensation of 4-4′-diaminodiphenylamino-2-sulfonate (DADPS) and 4-4′-diaminodiphenyloxide, taken in different ratios, with isophthaloylchloride) has been made. Knowledge of the factors controlling sorption and diffusion for water molecules as compared with alcohol molecules within polyamide films has stimulated the development of pervaporation (PV) membranes prepared from Na salt poly-4,4′-diphenylphthalamide-2,2′-disulfonic acid. The new PV membrane (Polar-22P) possesses the highest selectivity for water transport (α=104–105) with dehydration of the water-organic mixtures (acetone, isopropanol, ethylacetate) and a high water flux (Q≈0.5−1 kg/m2 h at 30 mol% H2O). The high local concentration of CO, the presence of sulfonic acid groups and organic cations on channel inlets and the inlet size are the factors regulating the high selectivity of water transport. The entrance of organic molecules such as isopropanol, acetone and ethylacetate into these channels becomes difficult due to the larger size of these molecules as compared with the inlet size.

Poly-N-vinylamides, complexation and conformational changes in aqueous solution

Abstract Interaction between small molecules (iodine and 1-anilinonaphthalene-8-sulphonate) and poly-N-methylacetamide (PVMA), poly-N-vinylcaprolactam (PVCL), poly-N-vinylpyrrolidone (PVP) and copolymers of N-vinyleaprolactam with N-vinylpyrrolidone (CP VCL-VP) and with N-vinyl-N-methylacetamide (VMA) were studied. All the polymers formed complexes with the small molecules. The stability constant for the complexes with the probe increases in the series PVMA M n changing from 6 × 103 to 2 × 103. Interaction of the polymers with I3− is accompanied by a conformational shrinking of coils. In the case of the probe, forces of electrostatic repulsion between negative charges of sulphonate groups result in an unfolding of polimer coils.